1. Field of the Invention
The present invention relates to an exposure apparatus which is used for transferring a pattern on a mask to a substrate, such as a wafer, in a photolithography process for producing semiconductors, liquid crystal displays, thin-film magnetic heads, etc.
2. Description of the Related Art
As exposure apparatuses used for producing, for example, semiconductors, there can be mentioned a projection exposure apparatus, such as a stepper, in which a reticle as a mask is illuminated with exposure light passing through an illumination optical system, to thereby transfer a pattern on the reticle through a projection optical system to a photoresist-coated wafer (or a glass plate), and an exposure apparatus of a proximity type or a contact type in which the pattern on the reticle is directly transferred to the wafer, using the above-mentioned exposure light. In these exposure apparatuses, ultraviolet light, such as an i-line from a super-high pressure mercury-vapor lamp (wavelength: 365 nm), has conventionally been used as exposure light.
In conventional exposure apparatuses, a series of lenses in the illumination optical system are divided into blocks and fixedly provided in lens barrels. In the illumination optical system, chambers defined by adjacent lenses are sealed by providing sealing materials between lenses and lens barrels. These sealing materials also serve as adhesives for fixing the lenses to the lens barrels. As such sealing materials, silicon-containing materials are generally used. In other words, in the sealed chambers in the illumination optical system, silicon-containing materials which serve not only as sealing materials, but also as adhesives are used. It is known that the sealing materials (or adhesives) containing silicon generate an organosilicon gas.
In conventional exposure apparatuses in which ultraviolet light is used as exposure light, ozone is produced from oxygen molecules in an atmosphere, in the presence of ultraviolet light. When an organosilicon gas is generated from the sealing materials (or adhesives) containing silicon, the ozone produced from oxygen in the presence of ultraviolet light oxidizes the organosilicon gas and consequently, deposition of haze substance, such as silicon dioxide (SiO2), on the surfaces of lenses is likely to occur. This leads to a lowering of illuminance of exposure light and a non-uniform distribution with respect to illuminance of exposure light. Because low molecular weight siloxane contained in the sealing materials (or adhesives) is a cause of the generation of organosilicon gas, in order to prevent deposition of SiO2 on the surfaces of lenses in an illumination optical system, recently, materials having a low content of low molecular weight siloxane have been used as the sealing materials (or adhesives).
Thus, in illumination optical systems in conventional exposure apparatuses, sealing materials (or adhesives) which are unlikely to generate an organosilicon gas, such as materials having a low content of low molecular weight siloxane, are used. However, such sealing materials exhibit poor operability due to a prolonged solidification time. Further, even when the content of low molecular weight siloxane in the sealing material is low, liberation of silicon cannot be completely suppressed, so that an organosilicon gas is generated in a small amount with a consequence that a small amount of SiO2 is likely to be deposited on the surface of lens.
As another example of sealing materials which are unlikely to generate an organosilicon gas, there can be mentioned non-evaporative two-liquid type adhesives. However, such two-liquid type adhesives also have poor operability.
Recently, there has been an increasing tendency to use, as exposure light, excimer laser beams having a short wavelength, such as a KrF excimer laserbeam (wavelength: 248 nm) and an ArF excimer laser beam (wavelength: 193 nm). On the other hand, it is known that when light having a short wavelength, such as excimer laser beams, is irradiated to adhesives containing silicon, silicon is liberated in a large amount. Therefore, it is considered that when excimer laser beams are used as exposure light, deposition of haze substance on the surfaces of lenses occurs in a wide range in the illumination optical system, so that countermeasures for deposition of haze substance have been strongly desired.
In view of the above situation, the present invention has been made. It is a primary object of the present invention to provide an exposure apparatus in which deposition of haze substance on optical members, such as lenses, in an illumination optical system can be suppressed, to thereby prevent a lowering of light transmittance and light reflectance of the lenses.
According to the present invention, there is provided an exposure apparatus for illuminating a pattern on a mask with exposure light passing through an illumination optical system, to thereby transfer the pattern on the mask to a substrate, comprising:
a sealed chamber provided in an optical path of the exposure light in the illumination optical system,
the sealed chamber containing a gas and shielded from a gas surrounding the sealed chamber in the illumination optical system; and
a gas exchanging device adapted to exchange the gas in the sealed chamber with a predetermined gas.
In the above-mentioned exposure apparatus, when an inert gas is contained in the sealed chamber, generation of ozone due to ultraviolet light which is used as exposure light can be avoided, so that even when an impurity gas, such as an organosilicon gas, is generated from sealing materials which are used in optical members (such as lenses) in contact with the gas in the sealed chamber, deposition of haze substance, such as SiO2, on the surfaces of optical members can be prevented. Further, when the gas in the sealed chamber is periodically exchanged with the predetermined gas, the impurity gas generated from the sealing materials can be removed. Due to the above two effects, occurrence of haze on the surfaces of optical members (leading to a lowering of light transmittance and light reflectance of the optical members) can be suppressed. As the inert gas contained in the sealed chamber, a high-purity nitrogen gas and a rare gas, such as helium, may be used.
In the above-mentioned exposure apparatus, it is preferred that the gas exchanging device comprise:
a gas exhausting system adapted to exhaust the gas in the sealed chamber;
a gas supplying system adapted to supply the predetermined gas to the sealed chamber;
a pressure sensor provided in the sealed chamber to detect a pressure in the sealed chamber; and
a control system adapted to control an operation of each of the gas exhausting system and the gas supplying system, based on the pressure in the sealed chamber detected by the pressure sensor, to thereby exchange the gas in the sealed chamber with the predetermined gas.
In the exposure apparatus having the gas exchanging device arranged as mentioned above, it is possible to exchange an impurity gas in the sealed chamber with an inert gas by repeating a gas exchanging operation in which a step of exhausting the impurity gas from the sealed chamber through the gas exhausting system and a step of supplying the inert gas through the gas supplying system to the sealed chamber are successively conducted.
In the present invention, it is more preferred that when the gas in the sealed chamber is exchanged with the predetermined gas, the control system enable the gas exhausting system to exhaust the gas in the sealed chamber and the gas supplying system to supply the predetermined gas to the sealed chamber, while maintaining an amount of change in the pressure in the sealed chamber detected by the pressure sensor within a predetermined allowable range. For example, an impurity gas in the sealed chamber may be exchanged with an inert gas by exhausting the impurity gas in an extremely small amount from the sealed chamber through the gas exhausting system and subsequently, supplying the inert gas in an amount equal to the amount of exhausted impurity gas through the gas supplying system to the sealed chamber so that a radical change in pressure in the sealed chamber can be suppressed. By this arrangement, stresses acting on lenses in contact with the gas in the sealed chamber become low, so that deterioration in performance of the illumination optical system can be avoided.
When the gas in the sealed chamber is exchanged with the predetermined gas with high frequency during assembly of the exposure apparatus, while suppressing a radical change in pressure in the sealed chamber, solidification of sealing materials (or adhesives) used in the lenses in contact with the gas in the sealed chamber is promoted, so that the time required for assembling the exposure apparatus can be reduced. In this case, because the gas exchange is conducted in a substantially stationary state with respect to the pressure in the sealed chamber, stresses acting on support members for supporting the lenses in contact with the gas in the sealed chamber are low and hence, damage to the lenses and deformation of the support members can be prevented. After operation of the exposure apparatus is started, it is preferred to exchange the gas in the sealed chamber periodically during idling of the exposure apparatus.
Further, in the present invention, it is preferred that the illumination optical system in the exposure apparatus comprise a light source adapted to emit exposure light, a shaping optical system adapted to shape the exposure light passing therethrough and an optical integrator adapted to enable the exposure light to have a uniform illuminance distribution after passing through the shaping optical system, and the sealed chamber be defined by two optical members constituting the shaping optical system. Because exposure light exhibits considerably high illuminance on a plane of incidence of the optical integrator, deposition of haze substance on the surfaces of lenses in the shaping optical system is likely to occur. However, by providing a sealed chamber defined by lenses in the shaping optical system and exchanging an impurity gas in the sealed chamber with a predetermined gas, the above-mentioned deposition of haze substance on the surfaces of lenses in the shaping optical system can be avoided.
Further, according to the present invention, there is provided a method for conducting an exchange of gases in a sealed chamber provided in an exposure apparatus, comprising a gas exchanging step including:
a first sub-step of exhausting a gas in the sealed chamber from a gas exhaust side thereof, while the sealed chamber is closed on a gas supply side thereof; and
a second sub-step of supplying an inert gas to the sealed chamber from the gas supply side thereof, while the sealed chamber is closed on the gas exhaust side thereof,
wherein each of the first sub-step and the second sub-step is conducted in a substantially stationary state with respect to a pressure of the gas in the sealed chamber.
Still further, according to the present invention, there is provided an exposure apparatus comprising:
an illumination optical system adapted to emit exposure light, the exposure light being adapted to illuminate a mask pattern to thereby transfer the mask pattern to a substrate;
a sealed chamber provided in the illumination optical system; and
a gas exchanging device adapted to exhaust a gas in the sealed chamber and supply an inert gas to the sealed chamber.
Still further, according to the present invention, there is provided a projection exposure apparatus for transferring a pattern on a mask to a photosensitive substrate, comprising:
a light source adapted to emit exposure light having a wavelength range in which a photosensitive substrate is sensitive to the exposure light;
an illumination optical system provided between the light source and the mask;
a projection optical system provided between the mask and the photosensitive substrate;
a sealed chamber containing a gas and provided in an optical path of the exposure light between the light source and the photosensitive substrate; and
a gas circulating device connected to the sealed chamber,
the gas circulating device being adapted to exhaust the gas contained in the sealed chamber to an outside thereof, to thereby compensate for variations in intensity of the exposure light on the photosensitive substrate.
Still further, according to the present invention, there is provided a projection exposure apparatus for transferring a pattern on a mask to a photosensitive substrate, comprising:
a light source adapted to emit exposure light having a wavelength range in which a photosensitive substrate is sensitive to the exposure light;
a sealed chamber provided in an optical path of the exposure light between the light source and the photosensitive substrate; and
a gas circulating device having a sensor and connected to the sealed chamber,
the sensor being adapted to detect and output information corresponding to a pressure in the sealed chamber, and
the gas circulating device being adapted to supply an inert gas to the sealed chamber in accordance with the information outputted from the sensor.
Still further, according to the present invention, there is provided a method for transferring a pattern on a mask to a photosensitive substrate, comprising the steps of:
illuminating the mask with exposure light, to thereby transfer the pattern on the mask to a photosensitive substrate; and
exchanging an inert gas contained in a sealed chamber with another gas,
the sealed chamber being provided in an optical path of the exposure light,
to thereby compensate for variations in light transmittance and light reflectance of an optical member provided in the optical path of the exposure light.
Still further, according to the present invention, there is provided an exposure apparatus for transferring a pattern on a mask to a photosensitive substrate, comprising:
an optical system adapted to allow exposure light to enter,
said exposure light being adapted to be irradiated to a photosensitive substrate; and
a device adapted to supply a gas capable of suppressing attenuation of said exposure light to said optical system, according to a change in light transmittance of said optical system which occurs due to entrance of said exposure light.
Still further, according to the present invention, there is provided a method for making an apparatus for transferring a pattern on a mask to a photosensitive substrate, comprising the steps of:
providing an optical system between a light source and a photosensitive substrate,
said light source being adapted to emit exposure light,
said exposure light being adapted to enter said optical system and irradiate said photosensitive substrate; and
providing a device adapted to supply a gas capable of suppressing attenuation of said exposure light to said optical system, according to a change in light transmittance of said optical system.
The foregoing and other objects, features and advantages of the present invention will be apparent from the following detailed description and appended claims taken in connection with the accompanying drawings.